1. Field of the Invention
The present invention relates to a second pole piece of a write head fabricated by high aspect ratio lithography and image transfer and, more particularly, to a highly defined second pole tip which is defined by a high aspect ratio negative photoresist strip wherein the image of the negative photoresist strip is transferred to an alumina frame for forming the second pole tip during a plating step.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The track width density of a write head is quantified as tracks per inch (TPI) along a radius of a rotating magnetic disk which is determined by the width of the second pole tip. The second pole tip is part of a second pole piece of the write head and is exposed at the ABS. If the second pole tip is made more narrow the storage capacity of the magnetic disk drive is increased. Efforts along this line, as well as increasing the number of bits written into the track along its length, have resulted in increasing the storage capacity of computers from kilobytes to megabytes to many gigabytes. The desire now is to fabricate second pole tips with submicron widths, which effort is limited by present fabrication techniques. The second pole tip is typically fabricated with a positive photoresist frame which has an opening where the second pole tip is to be formed. The resolution of the framing step for the second pole tip can be improved as will be discussed in the Summary of the Invention.
In order to mimimize side writing between the second pole tip and a first pole tip of the write head, it is desirable to notch the first pole tip on each side of the second pole tip so that the first pole tip has first and second side walls which align with first and second side walls respectively of the second pole tip. With this arrangement flux will be transferred between the first and second pole tips without extending side-wise beyond the first and second side walls of the first pole tip. Side writing expands the width of a track and reduces the track width density capability of the write head or, alternatively, write signals stray into adjacent tracks which degrades the signal performance of the rotating disk when the tracks are read by the read head. Typically, the first pole tip is notched by ion milling employing the second pole tip as a mask; This processing is detrimental to the second pole tip since the ion milling alters the height of the second pole tip as well as altering the composition and width of the second pole tip. Since the second pole tip is the last one of the first and second pole tips to pass by the rotating magnetic disk its resolution is extremely important for improving track width density of the write head.
In the present invention a strip of negative photoresist is formed on a wafer at an ABS site of the ABS with a width that defines a track width of a second pole tip and with a height which is above a desired height of the second pole tip. An alumina layer is then formed on the wafer and on the strip with a thickness above the wafer that is equal to or greater than a desired height of the second pole tip. The alumina layer is then chemically mechanically polished (CMP) until the negative photoresist strip is exposed. The negative photoresist strip is then removed leaving an opening for the second pole tip in the alumina layer. Employing the alumina layer as a frame the second pole tip is then plated in the opening. It has been found that the negative photoresist improves the aspect ratio of the lithography. The aspect ratio is the ratio of the width of the defining photoresist to its height. The aspect ratio of the aforementioned positive photoresist frame is the width of the opening in the positive photoresist to the height of the opening whereas the aspect ratio of the negative photoresist strip is the ratio of the width of the strip to its height. The resolution of the space in a positive photoresist frame is less than the resolution of the negative photoresist strip. For example, in order to produce a 0.6 xcexcm space in positive photoresist a 0.45 xcexcm mask opening would be employed during the light imaging step whereas in order to produce a 0.6 xcexcm negative resist strip it would be necessary to employ a 0.75 xcexcm mask during the light imaging step. The larger mask dimension is easier to make and the sigma (standard deviation) or windage is proportionately smaller.
While the photoresist strip can be fabricated from positive photoresist it is preferred that it be fabricated from negative photoresist. A negative photoresist strip has a greater structural integrity than a positive photoresist strip and can therefore be narrower, for increasing the TPI, and higher for fabricating a second pole tip with sufficient volume for carrying the required amount of flux. The high structural integrity of the negative photoresist strip is highly beneficial for constructing first and second notches in the first pole tip by ion milling. Instead of employing the second pole tip as a mask for constructing these notches the negative photoresist strip serves as the mask, thus preventing damage to the second pole tip.
In a preferred embodiment of the invention the first pole piece layer is provided with a first pole piece (P1) pedestal which extends upwardly from the first pole piece to a height greater than a write coil and the insulation thereon. The write coil layer is fabricated on an insulation layer which is on the first pole piece layer and an alumina layer is deposited on the entire wafer. The alumina layer is then chemically mechanically polished leaving some of the alumina insulation above the write coil layer and until a top surface of the P1 pedestal is exposed. A write gap layer is then deposited and a negative photoresist layer is deposited on the write gap layer. The negative photoresist layer is then light imaged and developed to provide two small openings at an ABS site with the openings being spaced apart by the desired negative photoresist strip width. The P1 pedestal can then be notched through the openings in the negative photoresist so that side edges of the notches line up with side edges of the negative photoresist strip. Alumina may then be deposited on the wafer with a thickness greater than the desired height of the second pole tip and chemically mechanically polished until the alumina is removed, except for first and 5 second alumina pedestals in the negative photoresist openings. The negative photoresist is then removed leaving a desired opening between first and second alumina pedestals for the fabrication of the second pole tip. A positive photoresist frame is then constructed for the second pole piece (P2) yoke after which the P2 tip and the P2 yoke are simultaneously plated between and back of the first and second alumina pedestals.
An object of the present invention is to fabricate a second pole tip of a write head with improved resolution.
Another object is to notch a first pole tip without damaging the second pole tip, especially when the second pole tip has a submicron track width.
A further object is to provide first and second embodiments of a write head which are fabricated by methods of the present invention.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.